1. Field of the Invention
The present invention relates to an aqueous dispersion coating material, and more particularly, relates to an aqueous dispersion coating material having an excellent corrosion resistance, storage stability and finished appearance and, furthermore, provides a coating adequate for a wide variety of coating applications.
2. Description of the Prior Art
In recent years, even in general industrial coating fields not employing an electro-deposition coating system because of environmental preservation and resource saving, it has become necessary to develop an aqueous coating material which is capable of providing a coated film having excellent corrosion resistance without using such harmful heavy metal system corrosion resistant pigments as chrome, lead and the like. Especially desired is the enhancement of the corrosion resistance of a coated film to be formed on so-called untreated iron surfaces which have not been chemically treated such as zinc phosphate or iron phosphate coated irons.
To cope with this kind of demand, a study has conventionally been made for achieving this improvement by improving the performance of the resin itself without relying upon corrosion resistant pigments, and the development of aqueous coating materials containing such resins having excellent corrosion resistance, such as maleinized polybutadiene resin, phenol-denatured water-soluble resins and epoxy-denatured resins which have been esterificated by ring-opening.
These types of aqueous coating materials are superior to aqueous coating materials containing simple polyester resins and acrylic system resins which are not denatured, but cannot satisfy the demands of a high level of corrosion resistance performance needed recently.
Japanese Patent Application Laid-Open No. 127359/1987 discloses that excellent corrosion resistance is provided by an aqueous dispersion coating material mainly consisting of an aqueous dispersion which can be obtained by compounding a special aqueous epoxy resin, mainly consisting of a bisphenol epoxy resin residue, with a solid epoxy resin having excellent corrosion resistance at normal temperatures.
The aqueous dispersion coating material proposed in the aforementioned patent application is higher in structural viscosity than conventional water-soluble coating materials, and for this reason, possesses the benefit that a thick film coating is available at the time of atomization coating by using an air spray or an airless spray on flat areas. However, the addition of this coating material to an organic solvent to control the structural viscosity of the aqueous coating materials, not only will bring about the aggregation of the dispersed particles but also deteriorates the storage stability of the coating material and, therefore, the structural viscosity cannot be controlled through the addition of organic solvents. If the coating material is applied without controlling the structural viscosity, liquid puddles and pinholes are caused to appear and degrade the appearance when using immersion coating or flow coating against vertical areas, which are widely used types of industrial coatings, and, therefore, there were problems such as the coating workability getting worse and the application of these types of coatings being difficult.